1. Field of the Invention
The present invention relates to a control device for controlling rigidity of a car body or deformation of a frame of a car body. An appropriate level of rigidity can be provided by the control device according to a form of collision of the car having a structure of absorbing an impact generated by collision.
The present application is based on Japanese Patent Applications No. Hei. 10-91552 and No. Hei. 10-206156, which are incorporated herein by reference.
2. Description of the Related Art
Since rigidity of a car body has an important effect upon safety of driving of the car, various countermeasures are taken for enhancing rigidity of the car. For example, frame members composing the car body are composed of steel plates of high strength, thickness of the frame members is increased, and reinforcement members are attached to appropriate portions of the frame members. At the same time, from the viewpoint of protecting passengers in the case of collision, it is desirable to provide a body structure capable of appropriately absorbing energy generated in collision. This absorption of impact energy generated in collision is mainly conducted by plastic deformation of a right and a left side frame extending in the longitudinal direction at the front portion of the car body. When rigidity of the side frames is appropriately set, deceleration generated in a passenger's chamber in the case of collision can be reduced, and the passenger is given an impact, the intensity of which is reduced.
In the case of a form of collision such as a front barrier collision in which the front surface of a car body collides entirely (this form of collision will be referred to as an overall collision in this specification hereinafter), an external force given to the car in collision is dispersed to the right and the left side frame. On the other hand, in the case of a form of collision such as an offset collision in which the front surface of a car body partially collides (this form of collision will be referred to as a partial collision in this specification hereinafter), an external force given to the car in collision is concentrated upon one of the side frames. For the above reasons, the following problems may be encountered. For example, when rigidity appropriate for partial collision is set in each side frame, the rigidity becomes too high when an impact of collision is absorbed in the case of an overall collision, and a high deceleration is generated. On the other hand, when rigidity appropriate for overall collision is set in each side frame, the rigidity becomes insufficient in the case of a partial collision, and an impact can not be sufficiently absorbed and the passenger's chamber is greatly affected by the collision. As described above, it is difficult to compose the side frames so that the most appropriate impact absorption can be conducted by them in both forms of collision.
Further, physical strength such as rigidity or breaking characteristic is affected by a stress-strain characteristic of material itself. Further, physical strength is affected by a sectional form represented by moment of inertia of area, and a shape in the longitudinal direction of a frame represented by a neutral axis of the frame. Furthermore, deformation of the frame is changed by an intensity and direction of an external force inputted into the frame, and a mechanical strength of the frame is greatly changed by a state of deformation. For example, when the frame is given an external force of a direction in which bending moment is generated in the frame, in many cases, the bending strength is insufficient compared with the compression strength. Therefore, buckling is caused in the frame. Accordingly, the mechanical strength is greatly insufficient compared with a case in which the frame is given an external force in the axial direction.
Consequently, in order to obtain predetermined rigidity and breaking characteristic, it is necessary to consider a state of deformation of the frame according to an intensity and direction of a predicted external force when a shape of the frame is designed. It is possible to optimize the shape of the frame by conducting a prediction in simulation or making experiments. However, from the actual viewpoint, it is very difficult to realize the most appropriate shape and state of deformation of the frame, because the manufacturing cost, space and weight are restricted.